Magneto Inductive, Flow Measuring Device

ABSTRACT

A magneto inductive, flow measuring device including a measuring tube and, arranged on the measuring tube, at least one magnet system, which includes a pole shoe. The measuring tube has at least one planar area and an otherwise cylindrical lateral surface, which border the measuring tube from its environment. The pole shoe is so formed relative to the measuring tube that it contacts the planar area of the measuring tube and has a predetermined minimum separation for the otherwise cylindrical lateral surface of the measuring tube. The pole shoe surrounds the measuring tube with a circular arc angle of at least 10°.

The present invention relates to a magneto inductive, flow measuringdevice having a measuring tube and at least one magnet system arrangedon the measuring tube.

Magneto inductive flow measuring devices utilize the principle ofelectrodynamic induction for volumetric flow measurement and are knownfrom a large number of publications. Charge carriers of the medium movedperpendicularly to a magnetic field induce a measurement voltage inmeasuring electrodes arranged essentially perpendicularly to the flowdirection of the medium and perpendicularly to the direction of themagnetic field. The measurement voltage induced in the measuringelectrodes is proportional to the flow velocity of the medium averagedover the cross section of the measuring tube, and is, thus, proportionalto the volume flow rate. If the density of the medium is known, the massflow in the pipeline, respectively in the measuring tube, can bedetermined. The measurement voltage is usually registered across ameasuring electrode pair, which is arranged relative to the coordinatealong the measuring tube axis in the region of maximum magnetic fieldstrength and where, thus, the maximum measurement voltage is to beexpected. The electrodes are usually galvanically coupled with themedium; there are, however, also magneto inductive, flow measuringdevices with contactless, capacitively coupling electrodes.

The measuring tube can, in such case, be manufactured either from anelectrically conductive, non-magnetic material, e.g. stainless steel, orfrom an electrically insulating material. If the measuring tube ismanufactured from an electrically conductive material, then it must belined in the region coming in contact with the medium with a liner of anelectrically insulating material. The liner is composed, depending ontemperature and medium, for example, of a thermoplastic, a thermosettingor an elastomeric, synthetic material, or plastic. There are, however,also magneto inductive, flow measuring devices, which have a ceramiclining.

Known from US 2004/0149046 A1 is an electromagnetic flow measuringdevice having a measuring tube, which has a planar area and an otherwisecylindrical surface. Arranged on the planar area is a pole shoe of amagnet system. In such case, the pole shoe, the inner core and the coilare secured on an outer core (for flux guide back) by a screwedconnection against slipping. Unfavorable in the case of this embodimentis the conventional flush, shape interlocking bearing of the pole shoeon the measuring tube, since this places high requirements ontolerances. Problematic is the mechanically little stable affixing ofthe pole shoe on the measuring tube only via the external core. This canlead in the case of vibrations to a degrading of the measurement signal.

U.S. Pat. No. 2,734,380 discloses a magnetic flow measuring devicehaving a measuring tube, in the case of which the pole shoes of twomagnet coils lie on a flat area. The two magnet cores are affixed on themeasuring tube by externally situated bolts (126 in the patent, FIG. 3).Disadvantageous in the case of this embodiment is that several bolts arenecessary and that, in the case of a non-symmetric tightening torque,additional measurement deviations can occur.

EP 1 674 836 A1 discloses a magneto inductive, flow measuring devicewith a coil and at least two components connected releasably with oneanother, wherein the component lies flat on a region of a right angledmeasurement line and is held by an external tube on this measurementline. Tolerances in the outer diameter of the measuring tube arecompensated, in such case, by a flexible piece of sheet metal, whichpresses the core and, via the core, the pole shoe against the measuringtube. Disadvantageous in the case of this embodiment is that the force,with which the sheet metal presses on the core, is relatively smallrelatively due to the thinness of the sheet metal, a feature which candisadvantageously influence the sensitivity of the measuring device andits stability e.g. in the case of vibrations.

U.S. Pat. No. 5,751,535 discloses an electronic flow measuring devicehaving a cylindrical measuring tube and pole shoes of a magnet bearingthereon. Disadvantageous in the case of these variants of embodiment areespecially the aperture angle of the pole shoe, which depends on thetube tolerances, since the bearing points are not defined via a planar,machined area, but, instead, via the contact of the pole shoes on theperiphery of the measuring tube. Depending on diameter or deviation fromideal roundness of the measuring tube, the bearing points of the poleshoe change on the measuring tube. When, in the mounting, the pole shoeis pressed against the measuring tube, the legs bend dependent on themeasuring tube geometry and the applied force. This can lead to anadditional measurement deviation.

DE 103 06 522 discloses a system for the efficient and guided mountingand affixing of a magnet system on a pipe of rather small diameter. Thisis especially achieved by an advantageous shaping of the coil form, thecoil core and the field guide-back path, and is less advantageous in thecase of greater tube diameters.

DE 35 45 155 discloses, among others things, the affixing of a magnetsystem on a housing composed of a number of parts, instead of directlyon the measuring tube (see FIG. 3 in the patent). Disadvantageous hereis that, depending on the dimensions and tolerances of the components, aseparation between pole shoe and measuring tube can occur or the housingdoes not fit over the core.

An electrode can be subdivided essentially into an electrode head, whichcomes in contact at least partially with a medium flowing through themeasuring tube, and an electrode shaft, which is situated almostcompletely in the wall of the measuring tube.

The electrodes are, besides the magnet system, the central components ofa magneto inductive, flow measuring device. In the embodiment andarrangement of the electrodes, attention is to be paid that they can beassembled in the measuring tube as simply as possible and thatsubsequently in measurement operation no sealing problems occur;moreover, the electrodes should provide a sensitive and simultaneouslylow-disturbance, registering of the measurement signal.

Besides the measuring electrodes, which serve for registering ameasurement signal, often additional electrodes are installed in themeasuring tube in the form of reference- or grounding electrodes. Theseserve to measure an electrical reference potential or to detectpartially filled measuring tubes or to register the temperature of themedium by means of an installed temperature sensor.

An object of the invention is to provide a simple and cost effectivelymanufactured, magneto inductive, flow measuring device.

The object is achieved by the features of the independent claims 1 and12. Further developments and embodiments of the invention are to befound in the features of the respective dependent claims.

The invention permits numerous forms of embodiment. Some thereof willnow be explained in greater detail based on the appended drawing, thefigures of which show as follows, wherein equal elements are providedwith equal reference characters:

FIG. 1 perspectively, a magneto inductive, flow measuring device of theinvention before the mounting of the magnet system,

FIG. 2 the magnet system of a magneto inductive, flow measuring deviceof the invention in an exploded view,

FIG. 3 in cross section, a magneto inductive, flow measuring device ofthe invention simplified in a sketch of principles, and

FIG. 4 a magneto inductive, flow measuring device of the invention in anadditional embodiment.

FIG. 1 shows perspectively individual assemblies of a magneto inductive,flow measuring device of the invention. A measuring tube 1 includes aplanar area 9 on an otherwise circularly cylindrical, lateral surface,and an essentially circularly shaped, inner diameter. Measuring tube 1is provided with this planar area 9, for example, by material removal,e.g. by milling material from the tube, or it can be originally soformed, e.g. cast, with the planar area 9. Especially, the measuringtube 1 has an otherwise circularly shaped cross section with a removedcircular segment, with the cross section of the planar area 9 as thechord limiting the circular segment. The lateral surface and the planararea 9 border the measuring tube externally from its environment.

Measuring tube 1 includes, here, end flanges 10. Placed in the measuringtube wall are, moreover, electrodes 13 and 15. In an example of anembodiment of the invention, the electrodes 13 and 15 contact themeasured material in the measuring tube 1. An electrode 15 protrudes, insuch case, outwardly from the planar area 9 of the measuring tube 1.This serves, for example, as a measured material monitoring electrode.

A second assembly is formed by a magnet system 2. Such includes a poleshoe 5 and a coil 3. Included supplementally here are a curved piece ofsheet metal, in the form of field guide-back 7, and a mounting clip 6.The magnet system 2 is described in detail in the description for FIG.2. It is, for example, arranged on the measuring tube 1 by beingsuperimposed on the planar area 9 and held pressed thereon with apredetermined force, such that it is, according to the invention,prestressed against the planar area 9.

In the shown further development, the magnet system 2 is prestressedagainst the planar area 9 of the measuring tube 1 by means of a mountingclip 6. Mounting clip 6 is here shape-interlocked with the flange 10 ofthe measuring tube 1. In this regard, flange 10 includes a cavity 11, inwhich the mounting clip 6 engages.

Mounting clip 6 is, thus, shape-interlocked with the measuring tube 1,here with its flanges 10, and the magnet system 2 is connected with themeasuring tube 1 by force interlocking, e.g. friction interlocking.Mounting clip 6 includes, in such case, a predetermined elasticity. Itserves as a resilient clamping element.

In the shown example of an embodiment, the force flux of the compressiveforce extends from the mounting clip 6 via the coil core 4 of the coil 3and the pole shoe 5 to the planar area 9 of the measuring tube 1.Arranged supplementally between mounting clip 6 and coil 3 is the fieldguide-back 7, through which the force is led. Mounting clip 6, fieldguide-back 7, coil 3 and pole shoe 5 are, in such case, connected withone another as an assembly via a screw 14. In an additional embodiment,the mounting clip 6 presses the coil core 4 of the coil 3 against thepole shoe 5 and this, thus, against the planar area 9 of the measuringtube 1.

Pole shoe 5, which is pressed against the planar area 9 of the measuringtube 1, is so formed, in such case, that it contacts the planar area 9of the measuring tube 1 and has a predetermined minimum separationgreater than zero from the otherwise cylindrical lateral surface of themeasuring tube 1. In such case, it surrounds the measuring tube 1 in acircular arc angle of at least 10°, especially at least 30°, forexample, even 60°. Here, the pole shoe 5 includes a planar area 16,which lies on the planar area 9 of the measuring tube 1.

The planar area 16 of the pole shoe 5 has here a width, which is greaterthan the width of the planar area 9 of the measuring tube 1. The widthsare, in such case, measured parallel to the planar area 9 of themeasuring tube 1 and orthogonally to the measuring tube axis of themeasuring tube 1 projected into the planar area 9 of the measuring tube.

Pole shoe 5 is constructed, for example, symmetrically, especiallymirror symmetrically, with a mirror plane, in which the measuring tubeaxis lies and which intersects the planar area 9 of the measuring tubeperpendicularly, and divides this, in such case, especially into twoequally large parts.

Here, the pole shoe 5 includes, bordering on the planar area 16, twolegs 17, each of which has the same angle from the planar area 16 andthe same size. Alternatively, the pole shoe 5 can have e.g. also twocircular arcs mounted on its planar area 16.

Shown is, furthermore, another electrode 13, which protrudes from themeasuring tube 1. Its longitudinal axis lies here in a plane parallel tothe planar surfaces 9 of the measuring tube 1. In such case, involvedare two measuring electrodes arranged in the measuring tube 1 and lyingopposite one another. The field guide-back 7 surrounds the measuringtube 1 in the mounted state in at least one plane perpendicular to themeasuring tube axis. In such case, also the measuring electrodes aresurrounded. Both field guide-backs 7 can, in such case, overlap and beconnected with one another, for example, by a screwed connection or anadditional, resiliently acting, mounting clip. This increases themechanical stability of the total system. As usual, the fieldguide-backs 7 surround the measuring tube 1 completely. The electrode 15extending out from the planar area 9 of the measuring tube 1 is here, incontrast, not surrounded by the field guide-back 7. It is axially offsetfrom the measuring electrodes and is externally shielded by the mountingclip 6 against mechanical influences, since such at least partiallycovers it on the side away from the measuring tube 1.

Not to be seen is that the measuring tube 1 has, in this furtherdevelopment of the invention, planparallel to the planar area 9, andtherewith also parallel to the measuring tube axis, another planar area,against which a further magnet system 2 is prestressed. The secondplanar area lies on the oppositely lying side of the measuring tube 1.It is otherwise identical to the first planar area 9. Also, the twomagnet systems 2 are equally constructed and produced, and are, thus,equally mounted. Because of the use of equal parts, such as e.g. coils,coil cores, pole shoes, field guide-backs and mounting clip, the magnetoinductive, flow measuring device of the invention is cost effective tomanufacture.

In a variant of the invention, the said components of the magnet systemare embodied in such a way that they are also combinable with similarlyconstructed, however, differently sized, components of a building blocksystem. Thus, different magnet systems for measuring tubes of differentdiameters or lengths can be manufactured simply and safely.

Another electrode can be provided for grounding. Alternatively, thegrounding is effected via the flanges 10 and the mounting clip 6contacting such, or, in an alternative embodiment, via the threaded pin18 connected electrically conductively with the measuring tube.

Moreover, signal cable for contacting the measuring electrodes is led,for example, through the coil core of the coil.

FIG. 2 shows, perspectively, a magnet system 2 of the invention for amagneto inductive, flow measuring device of the invention. It includes acoil 3 and a pole shoe 5. In the illustrated example of an embodiment,it includes, supplementally, a coil core 4 and a field guide-back 7 anda screw 14. Quite usual is also a coil core as an integral component ofthe pole shoe. The coil 3 includes here a coil form 23, around whichwire of electrically conductive material, e.g. copper wire, is wound.Arranged on the coil form 23 is a plug connector element 8 for theelectrical connection of the coil 3. Plug connector element 8 isarranged in the mounted state between the mounting clip 6 and themeasuring tube 1, and is, thus, protected against mechanical influencesexternally by the mounting clip, since it is at least partially shieldedby this.

Pole shoe 5 includes a pin or, such as here, a socket with internalthread 12, by which the coil 3 and, in given cases, a coil core 4 can beapplied. In the mounting, the pole shoe 5 is so oriented relative to themeasuring tube 1 that the threaded socket 12 has a longitudinal axis,which coincides with a diameter of the measuring tube 1.

Pole shoe 5, coil 3 and coil core 4 are affixed by means of the screw14, which is screwed into the threaded socket 12. Between coil 3,respectively coil core 4, and the head of the screw 14, the fieldguide-back 7 and the mounting clip 6 become clamped for producing themagnet system 2.

Two lines, which lie in a plane perpendicular to the measuring tubeaxis, and which connect the measuring tube axis with the respective endsof the pole shoe 5, define a circular arc angle α. This is illustratedin the sketch of principles, as presented in FIG. 3, wherein the planeof the drawing is the plane perpendicular to the measuring tube axis, inwhich the two lines lie, which enclose the circular arc angle α. Animaginary symmetry plane (not shown) divides the circular arc angle, inturn, into two equally large parts, wherein the measuring tube axis liesin the symmetry plane. Here, the symmetry plane is a symmetry plane withregard to both the measuring tube 1 as well as also the pole shoe 5.Pole shoe 5 surrounds the measuring tube 1 with a circular arc angle αof 0° to 180°, typically of 10° to 120°. If a pole shoe 5 is, such asshown here, composed of three planar surfaces 16 and 17, the middleplanar area 16 of the pole shoe 5, which in the mounted state contactsthe planar area of the measuring tube 1, surrounds the measuring tube 1with a first circular arc angle of, for example, 10°, wherein then theentire pole shoe surrounds the measuring tube 1 with a second circulararc angle of typically 15°.

The first angle, in such case, is between the two upturns (or downturns,depending on how one views it) on the two sides of the pole shoe, whilethe second is between the ends of the pole shoe. The first angle is, insuch case, typically —, however, not absolutely—at least as large as theangle subtended by the planar area 9 as defined from the measuring tubeaxis, wherein one considers for this the width of the planar area 9perpendicular to the measuring tube longitudinal axis as a circularsegment of the measuring tube cross section perpendicular to themeasuring tube longitudinal axis. Instead of one angling, a number ofother, incrementally angled upturns/downturns provide options or anycurving of the pole shoe to surround the measuring tube partially andcontoured with a predetermined minimum separation from the lateralsurface of the measuring tube and a maximum separation limited, amongother things, by the housing dimensions of the measuring transducer.

FIG. 4 shows a further embodiment of a magneto inductive, flow measuringdevice of the invention. The planar area 9 includes, according to theillustrated embodiment, axial shoulders 20, so that the complementarymagnet system 2, in the mounted state, rests against the axial shoulders20. The planar area 9 extends, thus, not, such as above, over the totallength of the measuring tube 1 between the two flanges 10. Here, theextent of the planar area in axial direction of the measuring tube 1,thus parallel to a longitudinal axis of the measuring tube 1, is limitedby the circularly cylindrical outer contour of the measuring tube,whereby the two axial stops 20 are formed. Alternatively, also at leastone axial stop, for example, in the form of a pin arranged on the planararea, can be provided on the planar area.

Pole shoe 5 has here additionally a length, which corresponds to thelength of the planar area 9 in the axial direction of the measuring tube1. Pole shoe 5, as part of the magnet system 2, is, thus, so formed forplanar area 9, that it is embodied in the region bearing on the planararea 9 to be complementary to the planar area 9. In the mounted state,it can, thus, not be moved in the axial direction of the measuring tube1 relative to the measuring tube 1. In the illustrated form ofembodiment, the axial shoulders 20 function supplementally as twistpreventers for the magnet system 2. By bearing against the shoulders 20,it cannot turn about an axis perpendicular to the planar area 9.

Protruding from the planar area 9 along this axis perpendicular toplanar area 9 is a threaded pin 18, which is connected fixedly with themeasuring tube 1. The magnet system is inserted onto the threaded pin 18and then clamped with a nut 19 turned to a predetermined torque. Also,here, thus, the magnet system 2 is pressed with a predetermined forceonto the measuring tube 1.

For this, the pole shoe 5 includes a bore 21, through which the threadedpin 18 is led. Also, the additional components or assemblies of themagnet system 2 are correspondingly formed. Thus, also the coil core andthe field guide-back have corresponding bores. An essential differencecompared to the above described example of an embodiment is, here, thatthe magnet system 2 is not separately assembled and mounted as anassembly on the measuring tube 1, but, instead, that the magnet system 2is mounted on the measuring tube 1 and, thus, assembled first on themeasuring tube 1.

By the provision of planar area 9 and pole shoe 5 embodied to becomplementary to one another, the danger is decisively lessened in themounting of the measuring device of the invention that parts not fittingone another might be used. The additional components of the magnetsystem 2 are likewise constructed corresponding to one another accordingto the idea of poka-yoke.

In the case of a pole shoe 5, which is designed for a certain diameterof the measuring tube 1, application in a magnet system for a devicewith a larger diameter of the measuring tube 1 is prevented, because theaperture angle α of the pole shoe 5 has a size, which, withoutconsiderable force on the pole shoe 5 perpendicular to the planar area9, does not permit the pole shoe 5 to contact the area 9. In the case ofa pole shoe 5, which is designed for a certain diameter of the measuringtube 1, application in a magnet system for a device with a smallerdiameter of the measuring tube 1 is prevented, because the axial lengthof the planar area 9 of a measuring tube 1 increases with the diameterof the measuring tube and the axial length of the pole shoe for acertain measuring tube, except for tolerance additions, which can begreater than or equal to zero, is the same as the axial length of thearea 9. Thus, a pole shoe 5 cannot lie completely on the planar area 9of a measuring tube 1, which has a smaller diameter than providedaccording to design of the pole shoe 5, since the axial length of thepole shoe 5 is too large for this. Thus, the two cases, the applicationof a pole shoe 5 for a device with larger measuring tube 1 as well asalso for a device with smaller measuring tube 1 than intended, areexcluded by the construction of pole shoe 5 and measuring tube 1 of theinvention.

In an additional preferred variant of the invention, the coil core 4 andthe pole shoe 5 are connected shape-interlocked with one another by apress fit.

Arranged around the coil core and over the pole shoe is the coilcomposed of coil form and winding. The coil form can in an embodiment bemounted with greater play in the direction of the longitudinal axis ofthe coil core, self-centered by the coil core. In this way,manufacturing tolerances can be advantageously absorbed.

The coil can supplementally also have detent means for accommodating,positioning and orientating the field guide-back 7 on the arrangement ofpole shoe, coil and coil core.

The arrangement of pole shoe, coil, coil core and field guide-back canpreferably be preassembled to a magnetic field producing module, whichis secured by the screwed connection onto the measuring tube. Themodular construction of this magnet apparatus reduces production effort,e.g. also in the case of mounting cables for signal transmission fromthe electrodes to the measurement transmitter through correspondinglyprovided openings for cable guidance in the interior of the fieldproducing module

In such case, the screwed connection can preferably be enabled via asingle, centrally arranged, threaded pin, which is secured directly tothe measuring tube, for example, by a welded connection. This reducesthe number of degrees of freedom in comparison with a plurality ofthreaded pins. Furthermore, a higher symmetry of the construction isachieved with less effort, which affects measurement deviationsadvantageously. At the same time, an increased compression is achievedin the relevant region of the junction between guide-back and coil core,which to leads improved signal level and signal stability.

For as simple as possible handling, the screwed connection is led, ineach case, preferably through the centers of the components of themagnet system, especially the coil, the coil core, the pole shoe and/orthe field guide-back.

Alternatively or supplementally, the affixing can occur by the earlierdescribed, mounting clip 6.

As already mentioned above, it especially advantageous, when the poleshoe of the magnet system is essentially sag and warp free, thus issecured without deformation on the measuring tube, so that no bendingrelated air gaps arise between the pole shoe and the coil core. The freespaces would lead to a reduction of the sensitivity of the sensor and toa change of the size of the air gaps due e.g. to temperaturefluctuations or vibrations, and this would lead to a change ofmeasurement deviation.

The prestressing occurs in the case of the screwed connection by adirect connection between the measuring tube and the magnet system. Insuch case, a threaded bolt is connected fixedly with the measuring tube,for example, by welding.

LIST OF REFERENCE CHARACTERS

-   1 measuring tube-   2 magnet system-   3 coil-   4 coil core-   5 pole shoe-   6 mounting clip-   7 field guide-back-   8 plug-   9 planar area of the measuring tube-   10 flange-   11 cavity-   12 threaded socket-   13 measuring electrode-   14 screw-   15 measured material monitoring electrode-   16 planar area of the pole shoe-   17 leg of the pole shoe-   18 threaded pin-   19 nut-   20 axial shoulder-   21 bore in the pole shoe for pass through of the threaded pin or the    threaded socket-   22 second planar area of the pole shoe-   23 coil form

1-14. (canceled)
 15. A magneto inductive flow measuring devicecomprising: a measuring tube, and arranged on said measuring tube, atleast one magnet system, which includes a pole shoe, wherein: saidmeasuring tube has at least one planar area and an otherwise cylindricallateral surface, which border said measuring tube from its environment;said pole shoe is so formed relative to said measuring tube that itcontacts said planar area of said measuring tube and has a predeterminedminimum separation from the otherwise cylindrical lateral surface ofsaid measuring tube; and said pole shoe surrounds said measuring tubewith a circular arc angle of at least 10°.
 16. The magneto inductive,flow measuring device as claimed in claim 15, wherein: said planar areaof said measuring tube has in the axial direction of said measuring tubean axial shoulder for said pole shoe.
 17. The magneto inductive, flowmeasuring device as claimed in claim 15, wherein: said planar area ofsaid measuring tube has a length axially of said measuring tube betweentwo axial shoulders; said pole shoe has a planar area, which has alength complementary to the length of said planar area of said measuringtube between said two axial shoulders, so that said pole shoe is axiallyoriented and affixed on said measuring tube.
 18. The magneto inductive,flow measuring device as claimed in claim 15, wherein: said pole shoehas a planar area, which is wider than said planar area of saidmeasuring tube.
 19. The magneto inductive, flow measuring device asclaimed in claim 15, wherein: an imaginary plane, in which the measuringtube axis lies, divides said planar area of said measuring tube into twoequally large parts; and said pole shoe is constructed mirrorsymmetrically about the imaginary plane as a mirror plane.
 20. Themagneto inductive, flow measuring device as claimed in claim 15,wherein: said pole shoe is prestressed with a predetermined forceagainst said planar area of said measuring tube.
 21. The magnetoinductive, flow measuring device as claimed in claim 20, wherein: saidmagnet system is prestressed against said planar area of said measuringtube by means of a mounting clip, which is secured shape-interlockedwith said measuring tube
 22. The magneto inductive, flow measuringdevice as claimed in claim 20, wherein: said magnet system isprestressed against said planar area of said measuring tube by means ofa screwed connection between said measuring tube and said magnet system.23. The magneto inductive, flow measuring device as claimed in claim 15,wherein: said measuring tube has, parallel to the measuring tube axisand planparallel to said planar area, another planar area; a furtherpole shoe of an additional magnet system is so formed relative to saidmeasuring tube that it contacts said other planar area of said measuringtube and has a predetermined minimum separation for the otherwisecylindrical lateral surface of said measuring tube; and said furtherpole shoe surrounds said measuring tube with a circular arc angle of atleast 10°.
 24. The magneto inductive, flow measuring device as claimedin claim 23, wherein: the two magnet systems comprise identicalassemblies.
 25. The magneto inductive, flow measuring device as claimedin claim 15, wherein: said magnet system includes a coil and a fieldguide-back sheet metal; and said field guide back completely surroundssaid measuring tube.
 26. A method for manufacturing a magneto inductiveflow measuring device as claimed in claim 15, providing the measuringtube with a circularly cylinder shaped lateral surface with a planararea; securing the pole shoe of the magnet system on the circularlycylinder shaped lateral surface; that it contacts the planar area of themeasuring tube and has a predetermined minimum separation from theotherwise cylindrical lateral surface of the measuring tube; andsurrounding the measuring tube with the pole shoe, with a circular arcangle of at least 10°.
 27. The method as claimed in claim 26, wherein: apreassembly of the magnet system first occurs and then the preassembledmagnet system is secured on the measuring tube by a mounting clip and/ora screwed connection.
 28. The method as claimed in claim 26, wherein:the magnet system is prestressed against a planar area of the measuringtube by means of a screwed connection between measuring tube and magnetsystem; and/or the magnet system is prestressed against a planar area ofthe measuring tube by means of the mounting clip, which is securedshape-interlocked to the measuring tube.